Allow comment lines in $$_dataServerRegistry.txt

[jmarshall]

I have IGV preferences set to point to my own Data Registry URL, which is a $$_dataServerRegistry.txt file with several extra dataset URL lines listing our local internal samples, etc.

It would be great if it were possible to quickly and easily switch datasets on and off, perhaps by commenting them out in the usual first-non-whitespace-character-is-# style. And being able to put comments in general in this file would occasionally be useful.

(I see one could put disabled datasets at the bottom of the file, offset from the enabled ones by a blank line or two. Is this the intended behaviour? It's not totally obvious that the break in LoadFromServerAction.java:getResourceUrls() might not be supposed to be a continue! )

[jsilter]

Added in commit 4339c56